Electric cable with expanded-metal shield and method of making

ABSTRACT

An electric cable has an expanded-metal tape bonded to a semiconducting polymeric shielding layer. The tape is slit and expanded during extrusion of the cable and continuously folded around the cable core.

United States Patent 1 Arnaudin, Jr.

1 ELECTRIC CABLE WITH EXPANDED-METAL SHIELD AND METHOD OF MAKING [75] Inventor: Edwin H. Amaudin, Jr., Eden, NC.

[73] Assignee: The Anaconda Company, New.

York, NY.

22 Filed: July 26, 1971 21 Appl.No.: 166,293

[52] US. Cl. 174/107; 29/624; 156/54;

174/36; 174/106 SC [51] Int. Cl. H01B 11/06 [58] Field of Search 174/36, 102 SC, 105 SC,

174/106 SC, 120 SC, 107, 102 SP, 73 R; 29/624, 6.1, 6.2, 163.5; 156/53, 54, 55, 56

[56] References Cited UNITED STATES PATENTS 2,939,905 6/1960 Canfield 174/107 X [451 Nov. 4, 1 975 3,332,138 7/1967 Garner....' 174/107 X 3,339,007 8/1967 Blodgett 174/102 D 3,433,687 3/1969 Price 174/102 SC X FOREIGN PATENTS OR APPLICATIONS 763,761 12/1956 United Kingdom 174/102 SC 239,349 12/1960 Australia 174/73 R 1,178,196 1/1970 United Kingdom 174/107 OTHER PUBLICATIONS R. C. Mildner, Bonded Jackets for Communication Cables, The Plastics Institute, April 1967, pp. 1-8.

Primary Examiner-Arthur T. Grimley Attorney, Agent, or FirmPennie & Edmonds [57] ABSTRACT An electric cable has an expanded-metal tape bonded to a semiconducting polymeric shielding layer. The tape is slit and expanded during extrusion of the cable and continuously folded around the cable core.

8 Claims, 3 Drawing Figures U.s.. Patent Nov;4,1975 3,917,900

T23 I I Fig 3 BACKGROUND OF THEINVENTION Electric cable having semiconducting polymericshielding reinforced with longitudinal drain wires are described in US. Pat. Nos. 3,473,189 and 3,571,613. In an earlier application (now U.S. Pat. No. 3,666,877) the present applicant has joined in describing a cable having foil strips bonded to the semiconducting composition. In these earlier structures there is no electrical connection between the metallic elements of the shielding except the semiconducting composition, which, of course, has limited conductivity. It would increase the overload conductivity of the shielding if the metal portionsweremetallically interconnected but no wayhas been heretofore suggested of achieving this desideratum at sufficiently low cost for material and manufacture. Particularly, an interconnected shielding structure has not been conceived that can be applied in a'single operation with the cableextrusion.

' SUMMARY 1 have invented an electric cable comprising an elongated conductor, a wall of insulation surrounding the conductor, a layer of semiconducting polymeric composition surrounding the wall of insulation and an expanded-metal tape surrounding the semiconducting layer. A coating of polymeric adhesive material is bonded to one or both surfaces of the tape and bonds the tape to the semiconducting layer. A polymeric jacket which may also be semiconducting is preferably extruded over the semiconducting layer and the expanded-metal tape may also be bonded to this jacket.

In my method of making a shielded cable I continuously pay a cable core comprising an outer semiconducting wall into an extrusion apparatus and concurrently pay an adhesive-coated metal tape into the apparatus. l continuously cut a plurality of slits into the tape and stretch the tape to open the slits and expand it. I continuously fold the expanded tape around the core and extrude a polymeric jacket around the core and the tape thereby also bonding the metal tape to the semiconducting wall. In my method the expanded-metal tape may be continuously flattened; and the semiconducting wall may be hot-extruded onto the core and the tape applied before the wall is cooled so that the adhesive is softened and bonds the expanded-metal tape to the semiconducting wall.

BRIEF DESCRIPTION OF THE DRAWING FIG. I shows the steps of the method of my invention.

FIG. 2 shows a pictorial cut-away view of a cable of my invention.

FIG. 3 shows a length of the tape used in the practice of my invention, prior to expanding.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 an extruder is shown having two heads ll, 12 for applying hot polymeric material in the manufacture of a cable. An insulated conductor 13 is seen paying into the head 11 wherein it receives a thin layer 14 (FIG. 2) of semiconducting polymeric material to form a core 16 which then pays into the head 12 where a polymeric jacket 17 is applied. In the illustration of FIG. 1

the material forming the layer 14 and jacket 17 is the same composition and a single extruder can be used. Where the jacket has a different composition, particularly where the jacket is not semiconducting, two different extruders may be used for feeding the heads 11 and 12. A supply 18 of metal tape 19, such as aluminum tape, is mounted to supply the tape to a point between the heads 11 and 12. In accordance with my invention this tape will advantageously be between 4 and 8 mils thick. It is also conceived to employ copper tape in which case the gage can be finer,'with a recommended thickness of 2% to 5 mils. As the tape 19 is paid from the supply 18 it passes through-a pair of rolls 21, 22 where it is slit in a cross-wise fashion as shown best in FIG. 3. Slits 23 made in the tape 19 are alternately staggered in a known manner for forming expanded metal. As shown in the drawing the slits are closed as formed by a thin bladed puncture. Where thicker punctures are used for cutting the tape, elongated apertures having appreciable openings will be formed, and the word slit as used in this application is inclusive of any suitable elongated aperture; The metal tape 19 has a backing or coating layer 24 of polymeric adhesive material such as the commercially available ethylene-acrylic acid copolymer disclosed in Pat. No. 3,315,025 to which conducting carbon black, graphite, or metallic particles have been added to make the adhesive semiconducting. The layer 24 has a thickness of 0.5 to about 2 mils and bonds firmly to the tape 19. The adhesive is dry and non-tacky at room temperature but will become tacky and bond firmly to polymeric cable insulation at extrusion temperatures.

On leaving the slitting rolls 21, 22 the tape 19 passes through pulling and flattening rolls 26, 27. Both the slitting and flattening rolls are driven by means not shown but the surface speed of the flattening rolls 26, 27 is sufficiently greater than the speed of the rolls 21, 22 to stretch the tape 19 and spread open each of the slits 23 to form diamond-shaped apertures 25 in a latticework of narrow interconnecting metal strips 28. The strips 28 are twisted, by the stretching action of the rolls, out of the plane of the tape 19, but are rolled flat again by the rolls 26, 27 Thereafter the tape 19 is folded around the core 16 by a folding die 29 and bonds weakly to the still-hot extruded layer 14. A thorough bond is completed, however, by the passage of the cable through the head 12 for application of the jacket 17. The completed cable is shown in FIG. 2 where a conductor 31, strand shielding 32, and extruded insulation 33 are conventional and the width of the expanded tape is sufficient completely to cover the core with a longitudinal, butt-lapped seam 36. Although I prefer to extrude the layer 14 of a semiconducting olefin polymer or copolymer, this shielding layer might also be applied in the form of a tape or hardenable fluid within the scope of my invention, the essential feature of which resides in the expanded metal shield 19. The expression expanded metal, as used in this application, has its art recognized meaning of a sheet that has been slit repeatedly through its thickness and subjected to tensile forces that pull the metal apart to form relatively large apertures from the slits. I have shown cross-wise slits in the tape 19. This has the advantage that the pulling tension to spread the slits can be applied by the same rolls that puncture the tape and those that flatten it. However, it is also within the scope of my invention to form the slits lengthwise of the tape and apply tension laterally in a continuous operation to expand the metal.

The foregoing description has been exemplary rather than definitive of my invention for which I desirean award of Letters Patent as defined in the following claims. I claim:

'I. An electric cable comprising:

A. an elongated conductor,

-B. a wall of insulation surrounding said conductor,

C. a layer of semiconducting polymeric composition surrounding said wall of insulation, D. a flattened expanded-metal tape surrounding said layer, B. a coating of polymeric adhesive material bonded to at least one surface of said tape, and bonding said tape to said layer.

2. The cable of claim 1 comprising a protective polymeric jacket surrounding said layer and said tape.

3. The cable of claim 1 wherein said tape comprises a'seam parallel to the axis of said cable.

4. The cable of claim 2 wherein said jacket is semiconducting. 1

5; The cable of claim 2 wherein layers of said material are bonded to both surfaces of said tape and said tape is bonded to said jacket.

6. The cable of claim 4 wherein layers of said material are-bonded to both surfaces of said tape and said tape is bonded to said jacket.

B. continuously concurrently paying an adhesivecoated metal tape into said apparatus, C. continuously concurrently cutting a plurality of slits into said tape,

D. continuously concurrently stretching said metal tape thereby opening said slits and expanding said metal tape,

E. continuously concurrently flattening said tape,

F. continuously concurrently folding the expandedmetal tape around said core, and

G. continuously concurrently extruding a polymeric jacket around said core and said expanded-metal tape thereby bonding said expanded-metal tape to said wall.

8. The method of claim 7 comprising the step of con:- tinuously hot-extruding said semiconducting wall andapplying the expanded-metal tape while said wall is retaining its heat of extrusion, said heat softening said adhesive and bonding the expanded-metal tape to said wall. 

1. An electric cable comprising: A. an elongated conductor, B. a wall of insulation surrounding said conductor, C. a layer of semiconducting polymeric composition surrounding said wall of insulation, D. a flattened expanded-metal tape surrounding said layer, E. a coating of polymeric adhesive material bonded to at least one surface of said tape, and bonding said tape to said layer.
 2. The cable of claim 1 comprising a protective polymeric jacket surrounding said layer and said tape.
 3. The cable of claim 1 wherein said tape comprises a seam parallel to the axis of said cable.
 4. The cable of claim 2 wherein said jacket is semiconducting.
 5. The cable of claim 2 wherein layers of said material are bonded to both surfaces of said tape and said tape is bonded to said jacket.
 6. The cable of claim 4 wherein layers of said material are bonded to both surfaces of said tape and said tape is bonded to said jacket.
 7. The method of making a shielded electric cable comprising the steps of: A. continuously paying a cable core comprising an outer semiconducting wall into an extrusion apparatus, B. continuously concurrently paying an adhesive-coated metal tape into said apparatus, C. continuously concurrently cutting a plurality of slits into said tape, D. continuously concurrently stretching said metal tape thereby opening said slits and expanding said metal tape, E. continuously concurrently flattening said tape, F. continuously concurrently folding the expanded-metal tape around said core, and G. continuously concurrently extruding a polymeric jacket around said core and said expanded-metal tape thereby bonding said expanded-metal tape to said wall.
 8. The method of claim 7 comprising the step of continuously hot-extruding said semiconducting wall and applying the expanded-metal tape while said wall is retaining its heat of extrusion, said heat softening said adhesive and bonding the expanded-metal tape to said wall. 